Jet fuel compositions containing alkylene biborates



United States Patent 3,009,799 JET FUEL COMROSiTIONS CQNTAINING ALKYLENE BIBORATES Fred J. Dykstra, Detroit, Mich, assignor to Ethyl Corporation, New York, N.Y., a corporation-of Delaware N Drawing. Filed May 14, 1956, Ser. No. 584,430

7 Claims. (Cl. 52.5)

This invention relates to new jet fuel compositions characterized by high thermal stability.

Fuel temperatures in modern jet aircraft power plants are becoming so high that harmful deposits are formed in the pre-combustion phase of the fuel system. Co-ntributing to this has been the use of the fuel as a heat sink to aid in lubricating oil cooling, which has increased fuel temperatures to the point where deposits are so severe that they interfere with normal fuel combustion as well as lubricating oil temperature control. This is so serious a problem that it can eventually lead to engine failure of the turbine section due to uneven temperature patterns. In fact, it is considered the outstanding problem in jet fuels at the present time. Attempts have been made to counteract this by redesigning and by the use of shielding materials to minimize heating of the fuel. These methods are uneconomical and also contribute substantially to the over-all weight of the aircraft.

An object of this invention is to alleviate the thermal stability problems in jet fuels. Another object is to provide new jet fuel compositions which are characterized by a high degree of thermal stability. A further object is to provide processes of inhibiting deterioration of jet fuel normally tending to occur at elevated temperatures below the cracking temperature of the fuel. Other objects will be apparent from the ensuing description.

- The above and other objects of this invention are accomplished by providing jet fuel containing from about 0.005 to about 5 percent by weight of an alkylene biborate, sometimes referred to as tri(alkylene)biborate,

in which each alkylene group contains from 2 to 20 carbon atoms and is from 2 to 6 carbon atoms in length. Such compositions, as will be seen below, have a thermal stability of a magnitude which is well beyond that now possessed by any other'commercial fuel.

It is known that conventional jet fuel normally tends to deteriorate when subjected to the condition of elevated temperatures below the cracking temperature of the fuel, i.e., temperatures in the range of about 300 to about 500 F. Thus, a part of this invention i the process of inhibiting such deterioration which comprises subjecting a jet fuel containing from about 0.005 to about 5 percent by weight of an alkylene biborate as'above defined to said condition. Thus, enhanced thermal stability of jet fuel is achieved by blending with a jet fuel from about 0.005

to about 5 percent by weight of an alkylene bibora-te as defined above and subjecting the resulting fuel to the above-condition.

The alkylene biborate jet fuel additives have the formula:

3,009,799 Patented Nov. 21, 1961 of dihydroxyalkane containing from 2 to -carbon atoms,

the two hydroxyl groups of which are separated by from 2 to 6 carbon atoms. Such alkane can also be substituted with other hydrocarbon groups, such as alkyl, cycloalkyl, aralkyl, aryl, and alkaryl. Generally speaking, the nature of such substituents in the alkane is immaterial so long as the total number of carbon atoms in the alkane is no greater than 20. The alkylene groups of the bi-borate esters can also contain one nitrogen atom; iminodit ethylene, iminodiisopropylene, N-ethyl iminodiethylene,

etc., serving as examples. These particular biborates are thus formed from 'tWo moles of a diol, such as diethanol amine, dipropanol amine, diisopropanol amine, N-ethyl diethanol amine, etc, per equivalent weight of biboric acid.

Preferred jet fuel additives of this invention are alkylene biborates containing a total of from 6 to, 16 carbon atoms wherein each alkylene. group is from 2 to 3 carbon atoms in length and is substituted with from 1 to 4 alkyl groups containing from 1 to 2 carbon atoms. These preferred bi'borates are thus alkylene biborates having two 5- or 6-mem=bered rings composed of two or three carbon atoms, two oxygen atoms and one boron atom. These biborates are preferred because they are miscible in all proportions with most jet fuels. Moreover, the S-for 6- membered rings in these preferred biborates impart a high degree of stability to the additives.

can be referred to as tri(ethylene glycollbiborate or as tri( 1,2-ethylene) biborate.

Similarly, the 'biborate having the following formula om n -o\" Cq CH 0----('JH 3 8 on, 1 H on 511C557 l O B on 2 2 n 11 01130-0 2 2 o-bn' can be referred to as tri(2,5-hexylene glycol )'biborate or tri(2,5-hexanediol)biborate or as tri(2,5-hexylene)biborate. The nomenclature of other esters of this invention follows the same pattern. Nomenclature of esters formed from more than one glycol (mixed esters) is similar except that the prefixes di and mono are used to indicate the number of each alkylene radical present.

Particularly preferred as a jet fuel "additive are vention is the fact that when, under drastic conditions,.

they are hydrolyzed the hydrolysis products thereof are themselves extremely resistant to hydrolysis and very soluble in the jet fuel. Consequently, even though a jet fuel composition of this invention is agitated with large quantitles of water, the boron dissolved in this fuel remains in solution in a'suitable chemical form and continues to exert its beneficial functions. Furthermore, such drastic hydrolysis conditions do not result in the formation of insoluble sludges or other residues which would normally occur when'using prior boron additives in jet fuels.

Still another feature of this invention is the fact that the pre'sentadditives are easily made and inexpensive. Thus, this invention enables substantial improvements in the performancecharacteristics of jet fuels at low' cost.

. The jet fuels Whose thermal stability is greatly improved pursuant to this invention, are principally hydrocarbon fuel which are heavier than gasoline, i.e., distilled liquid hydrocarbon fuels having a higher endpoint than gasoline. In general, the jet fuels canbe comprised of distillate fuels and naphthas and blends of the above, including blends with lighter hydrocarbon fractions, so long as the endpoint of the final jet fuel is at least 435 F. and prefer ably greater than 480 F. It will be understood, however, that the jet fuels which are employed according to this invention can contain certain other ingredients such as alcohols or the like, provided the resulting fuel blend meets the specifications imposed upon jet fuels. However, the jet fuels of this invention are free of organo metallic additives because such additives interfere with the ability of the biborates to improve the thermal stability properties of the fuels. Thus, an organorn-etallic additive, if present in the jet fuel, would counteract the effectiveness of the biborate additive and render the jet fuel at least as thermally unstable as it would be in the absence of any additive. This counteraction of effectiveness is attributable, at ieast in part, to the thermal degradation of the organometallic additive itself and the designed for high altitude performance; JP-S, an especially' fractionated kerosene; low freezing point kerosene, etc.

The following are specifications of typical liquid hydrocarbon jet fuels of this invention:

' Fuel E Fuel F Fuel A Fuel B Fuel 0 Fuel D (JP-4 (kero- (J P-3) (.T 13-4) (JP5) (JP-4) refsene) eree) 10% evaporated, F. 160 220 395 221 380 90% evaporated, F- 470 470 480 379 460 480 Endpoint, F 600 550 550 480 516 Gravity, A1 1... 50 45 47. 3 48. 5 43 Existent gum, mg./

100 ml., max 7 7 7 1. 0 1.4 1.7 Potential gum, rug/100 mL, max- 14 14 14 1. 0 9. 6 Reid vapor pressure, p.s.i. 7. 0 3.0 Aromatics, vol.

percent 25. 0 25.0 25. 0 12.5 14. 6 14. 3 Olefins, vol. percent.. 5.0 5.0 5.0 0.3 1.2

' 4 The following examples illustrate various specific embodiments of this invention.

Example I To 100,000 parts of Fuel A is added with stirring five parts (0.005 percent) of tri(ethylene glycol)biborate dissolved in 50 parts of toluene. The resulting fuel is found to possess improved thermal stability characteristics.

Example II To 100,000 parts of Fuel B is added 5000 parts (5 percent) or tri(1 ,2propylene glycol)biborate. The resulting fuel possesses improved thermal stability properties.

Example III To 100,000 parts of Fuel C is added part (0.1 percent) of tri(l,3-propylene glycol)biborate dissolved in 1000 parts of xylene. The resulting fuel blend possesses superior thermal stability characteristics.

Example IV To 100,000 parts of Fuel D is added 500 parts (0.5 percent) of tri(l,4-butanediol)biborate. The resulting fuel blend is found to possess superior thermal stability characteristics.

Example V To 100,000 parts of Fuel E is added 40 parts (0.04 percent) of tri(l,4-butanediol)biborate dissolved in 600 parts of benzene. The resulting fuel blend possesses enhanced thermal stability properties.

Example VI To 100,000 parts of Fuel F is added 200 parts (0.2 percent) of tri(1,6-hexylene glycol)biborate dissolved in 5000 parts of toluene. After mixing, the resulting fuel blend is found to possess enhanced thermal stability properties.

Example VII Fuel C is blended with a lighter hydrocarbon fraction to give a final jet fuel having an endpoint of 435 F. 100,000 parts of this fuel is treated with 20 parts (0.02 percent) of tri(2,4-hexylene :glycoUbiborate. The resulting clearfuel possesses outstanding thermal stability characteristics.

Example IX To 100,000 parts of Fuel A is added 15 parts (0.015 percent) of tri(2-methyl-2,4-pentanediol)biborate. This fuel after mixing, possesses outstanding thermal stability characteristics.

Example X Fifty parts of tri(2,5-dimethyl-2,5-hexylene glycol)- bibora-te is blended with 100,000 parts of Fuel B. The resulting'jet fuel blend containing 0.05 percent of the biborate possesses outstanding thermal stability characteri-stics.

Example XI To 100,000 parts of Fuel C is added 4000 parts (4 percent) of tri(l,S-diphenyl-B-isopropyl-1,5-pentanediol) biborate. The resulting jet fuel blend possesses eminently superior thermal stability characteristics.

Example XII To 100,000 parts of Pool B is added with stirring l0 parts (0.01 percent) of tri(3-cyclohexyl-2,4-octanediol)- biborate. The resulting jet fuel is found to possess outstanding thermal stability characteristics.

Example XIII .To 100,000 parts of Fuel 1) is added 100 parts 0.1 percent) of tri(Z-benzyl-1,3-propanediol)biborate. After stirring, the resulting clear fuel possesses enhanced thermal stability characteristics.

Example XIV Example XV To 100,000 parts of Fuel A is added 100 parts (0.1 percent) of tri(2,3-pentanediol)biborate. The resulting fuel possesses improved thermal stability characteristics.

Example XVI To 100,000 parts of Fuel C is added 500 parts (0.5 percent) of tri(2,4-dimethyl-2,4-pent-anediol)biborate. The

resulting fuel blend possesses outstanding thermal stability characteristics.

ing fuel possesses outstanding thermal stability properties.

The substantial improvements which result from addition of alkylene biborates, as described above, to jet fuel is illustrated by tests in an apparatus known as the Erdco Fuel Coker. See Petroleum Processing, December 1955, pages 1909-1901. The apparatus consists of aheated, sintered steel filter through which a pre-heaited fuel is passed at a regulated rate. The time which it takes for the pressure drop across the filter to reach 25 inches of mercury is taken as a measurement of the coking tendencies of the fuel and, therefore, as a measurement of the thermal stability characteristics of the fuel. A fuel that runs through the apparatus for a full 300 minutes without causing any pressure drop is considered completely, thermally stable. The ideal fuel would pass through the filter indefinitely without causing any pressure drop.

To demonstrate the substantial improvements in high temperature stability exhibited in jet fuels of this invention, recourse is had to the above Erdco Coking test. Samples of jet fuels of this invention, such as those appearing in the above examples, are subjected to the Erdco Coking test. The conditions used in this test are as follows: 'Unit operated at 150 psi. with the pre-heater temperature at 325 F., the filter temperature at 500 F., and a residence time of 30 seconds. For comparative purposes, the corresponding biborate-free base fuels are likewise subjected to this test. It is found that in all instances the presence in the fuels of the biborate causes a substantial increase in the time required for a pressure drop of 25 inches of mercury across thefi'lter to occur. Furthermore, the majority of the fuels of this invention formulated from base fuels requiring at least 150 minutes for this pressure drop to occur do not reach this pressure drop even in the full 300 minutes. In some cases, the pressure drop achieved with these last-named jet fuels of this invention is less than inches of mercury after 300 minutes.

As an example of the outstanding potency of alkylene biborates in improving the high temperature stability characteristics of jet fuels, comparative Erdco Coking tests are conducted under the conditions specified above.

.The base fuel used is a JP-4 referee fuel having the following inspection data:

Gravity, API 48.5 Vapor pressure 2.8 Distillation, initial, F.:

460 Final 516 Existent gum, mg./ ml 1.4 Potential gum, mg./ l00ml 9.6 Total sulfur, perc n p 0.193 Mercaptan sulfur, percent 0.001 Freezing point, F ,-67 v Aromatic, vol. percent 14.6 Olefins, vol. percent-.. 1.2

When this additive-free base fuel is tested for its thermal stability in a pair of tests, it was found that a pressure drop of 25 inches of mercury occurred' after 27 and 32 minutes. Two individual portions of this same base fuel, each containing 0.17 percent by weight of alkylene biborate; such as tri(propylene. glycol)biborate, show a substantial increase in the time to .this pressure drop. Thus, typical fuels of this invention possess a thermal stability substantially greater than the corresponding biboratefree base fuel.

Similar results are obtained with other jet fuel compositions of this invention, i.e., hydrocarbon jet fuels cont-aining from about 0.005 to about 5 percent by weight of any biborate described by the general formula appearing above.

The jet fuel compositions of this invention possess outstanding high temperature stability characteristics by the presence therein of such additives as tri(ethylene glycol)- bibor ate, tri( 1,2-propylene glycol)biborate, tri( 1,3-propylene glycol)biborate, tni(l,2-butylene glycol)biborate, tri- (1,3-butylene glycol)biborate, tri(1,4-butylene glycol)- bibora-te, tri( 1,6-hexylene glycol)bi-borate, tri(2,4-dimethyl 2,4 pentanediol)biborate, tri(2,3 dibutyltetramethylene glycol)biborate, tri(2,3-diphenyl tetramethylene glycol)bib0nate, and the like.

The additives of this invention can be conveniently prepared by heating boric acid or boric oxide with the appropriate glycol as defined above, in the ratio of substantially two moles of boric acid or one mole of boric oxide to three moles of the glycol. The reaction is preferably conducted at temperatures under which the water of estenification is driven oif as vapor and not permitted to return to the reaction mixture, thus hastening the reaction to completion. It is convenient to use an azeotroping agent such as an aromatic hydrocarbon (benzene, toluene, etc.) to facilitate water removal. This method using boric-acid is described in the Journal of the American Chemical Society, volume 67, pages 879-880 (1945).

The following example illustrates preparation of a typical biborate of this invention starting with boric oxide.

Example XVIII Boric oxide (B 0 70 parts) and 2-methyl-2,4-pentanediol (39.5 parts) were heated together in toluene medium in a system provided with a reflux condenser to which was attached a water trap. Heating was continued for a period of 30 minutes during which time 5.6 parts of water were taken off in the trap. The residual reaction mixture was then freed of toluene by distillation at about 3 millimeters. The tri(2- methyl-2,4-pentanediol)biborate product was recovered as residue from this distillation. Analysis of the material showed a boron content of 5.70 percent (calculated 5.85 percent).

The other biborate esters of this invention are prepared to 0.2 percent are found to be quite efiective.

, 7 by the above two methods, varying only the starting materials and the reaction temperature in order to operate preferably at the reflux temperature of the system at the pressure employed.

The amount of alkylene biborate used in the jet fuels of this invention can range from about 0.005 percent to about 5 percent by weight. Ordinarily, amounts of 001 Variations from these concentration ranges are permissible. For example, in jet fuels initially possessing afair degree of thermal stability,rvery srnall amounts of the above biborates are sufiicient to greatly improve the thermal stability characteristics oi such fuels On the other hand, where the jet'fuel initially has a very poor thermal stability,

. larger amounts (about 4 to 5 percent by weight or more) can be effectively used.

carbon atoms in length. 7

2. Jet fuel consisting essentially of a distilled liquid hydrocarbon fuel having an end point of at least 480 F. containing from about 0.005 to about 5 percent by weight of an alkylene bi-bora-te containing a total of from 6 to 16 carbon atoms wherein each alkylene group is from 2 to 3 carbon atoms in length and is substituted with from 1 to 4 alkyl groups containing from 1 to 2 carbon atoms.

3. The composition of claim 2 in which the biborate is tri-(1,3-butylene glycol) biboralte.

4. The composition of claim 2 in which the bi-borate is tri-(2methyl-2,4-pentanediol) biborate.

r 5. The composition of claim 2 in which the biborate is tri-(2,4-hexylene glycol) biborate.

6. Jet fuel consisting essentially of a distilled liquid hydrocarbon fuel having an end point of at least 480 F. said end point being higher than that of gasoline containing from about 0.005 to about 5 percent by weight of tri(propylene glycol)biborate.

7. A process for cooling the lubricating oil in a jet engine by utilizing as a heat sink a jet fuel consisting essentially of distilled liquid hydrocarbon fuel having an end point of at least 435 F., said end point being higher than that of gasoline, said fuel containing from about 0.005 to about 5 percent 'by weight of an alkylene biborate in which each alkylene group contains from 2-20 carbon atoms and is from 2-6 carbon atoms in length.

References Cited in the file of this patent UNITED STATES PATENTS 2,710,252 Darling June 7, 1955 2,741,548 Darling et a]. Apr. 10, I956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 3 OO9 799 November 21 1961 Fred Jo Dykstra It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 7 lines 19 and 25,, after "480 Ffl each occurrence, insert said end point being higher than that of gasoline Signed and sealed this 5th day of June 1962(,

(SEAL) Attest:

ERNEST w. SWIDER DAVID A attesting Officer Commissioner of Patents 

1. JET FUEL CONSISTING ESSENTIALLY OF A DISTILLED LIQUID HYDROCARBON FUEL HAVING AN END POINT OF AT LEAST 480*F. CONTAINING FROM ABOUT 0.005 TO ABOUT 5 PERCENT BY WEIGHT OF AN ALKYLENE BIBORATE IN WHICH EACH ALKYLENE GROUP CONTAINS FROM 2 TO 20 CARBON ATOMS AND IS FROM 2 TO 6 CARBON ATOMS IN LENGTH. 